The present invention is related to Japanese patent application No. 2000-220129, filed Jul. 21, 2000; the contents of which are incorporated herein by reference.
The present invention relates to an accumulator fuel injection apparatus for internal combustion engines, and more particularly, to an accumulator fuel injection apparatus for internal combustion engines provided with a pressure safety valve which is opened when an accumulator pressure has exceeded a preset value to thereby lower the accumulator pressure below the excess pressure.
There has been generally known an accumulator fuel injection apparatus for internal combustion engines in which high-pressure fuel is pressurized and accumulated in an accumulator by means of a high-pressure feed pump. The high-pressure fuel thus accumulated in t he accumulator is distributed to a plurality of fuel injection valves installed in each cylinder of a vehicle-mounted internal combustion engine, then injected from the plurality of fuel injection valves into each cylinder of the internal combustion engine. The accumulator fuel injection apparatus for internal combustion engines is generally provided with a pressure safety valve in the end part of the accumulator.
The pressure safety valve, as shown in FIG. 4, operates to insure safety by preventing fuel leakage from each part in an emergency when an excessive quantity of high-pressure fuel is forced into the fuel supply line ranging from the high-pressure feed pump to the accumulator. FIG. 4A shows a behavior of the accumulator fuel pressure when the motor vehicle is driven to a turnout (a turnout being any diversion from a main road to a outside lane, turnout or other side-of-the road area) in an emergency, and FIG. 4B shows a behavior of the high-pressure fuel feed pump to be operated in case of an emergency driving to a turnout.
When the motor vehicle is driven from a driving or passing lane to a shoulder in an emergency driving in a turnout which requires excessive fuel to be supplied from the high-pressure fuel feed pump, the valve element of the pressure safety valve moves away from the valve seat to open the valve in a conventional fuel injection apparatus. In this case, however, the accumulator pressure is released, thereby lowering the pressure less than the excessive pressure and the operating pressure of the injector. Therefore, fuel injection from the injector into each cylinder of the internal combustion chamber will fail, causing the motor vehicle to be unable to drive to the turnout even when an emergency demands such.
For the purpose of solving the above-described problem of excessive pressure supply from the high-pressure fuel feed pump to drive the motor vehicle to a turnout in an emergency, there has been proposed such a device as disclosed in JP-A No. H4-72454, which produces a valve opening pressure required to prevent an accumulator pressure rise over a predetermined value and a valve closing pressure required to accomplish the emergency driving of the motor vehicle to the turnout.
In a conventional accumulator fuel injection apparatus for internal combustion engines, when an injection interval of the high-pressure fuel feed pump exceeds a predetermined interval, for example during the low-speed rotation of the internal combustion engine and the high-pressure fuel feed pump, the interval is relatively wide. During this interval, therefore, the accumulator pressure is likely to drop excessively low. Therefore the valve element of the pressure safety valve seats on the valve seat to close the valve. At this time, because the high-pressure fuel feed pump is in operation, the discharge pressure being discharged from the high-pressure fuel feed pump into the accumulator increases (the forced supply of excessive fuel remains unreleased at this point of time), and therefore the valve will open if the accumulator pressure increases again over the valve element opening pressure of the pressure safety valve, thus repeating the low-speed operation of the internal combustion engine.
Therefore, as shown in FIG. 4, the accumulator pressure varies as low as the value of the excessively lowered pressure below the valve opening pressure. It is, therefore, impossible to stabilize the accumulator pressure at a value (a regulated pressure) necessary for moving the motor vehicle in the event of emergency driving to a turnout. At this time the motor vehicle runs at a low speed such that noises and knocks occur, giving the driver (the user) discomfort.
It is therefore an object of the invention to provide an accumulator fuel injection apparatus for internal combustion engines implementing a pressure safety valve which allows smooth running of the motor vehicle to the turnout lane in an emergency by stabilizing the pressure necessary for emergency driving to the turnout to a low pressure at which no noise and knock will occur.
According to a first aspect of this invention, in an emergency where excessive pressure fuel is delivered from the high-pressure fuel feed pump, the accumulator pressure is increased by the excessive pressure of the high-pressure fuel feed pump. When the accumulator pressure has exceeded a predetermined value to overcome the spring force of the pressure safety valve, the valve element of the pressure safety valve and the piston rise off the valve seat of the valve body. Thus, the valve element opens the valve port of the valve body, releasing the abnormally high pressure which can cause fuel leaks, thereby enabling to insure safety against the abnormally high pressure.
To drive the motor vehicle to the turnout lane in an emergency as described above, the fuel pressure necessary for turning out the motor vehicle is increased higher than the fuel injection valve operating pressure to thereby enable fuel injection from the fuel injection valve to each cylinder, and also the pressure is decreased to a value at which no noise and knock will occur, to achieve driving stability. Then, on the downstream side of the sliding bore in the valve body of the pressure safety valve, a damper chamber is formed to house both the large-diameter portion of the pressure safety valve piston and the fuel, so that the downward speed of the valve element and piston, when displaced by the spring force toward the valve-closing side, is restrained, resulting in a prolonged time of downward movement of the valve element and the piston.
Therefore, if the internal combustion engine and the high-pressure fuel feed pump are operating at low speeds, the valve element can be held off the valve seat until the beginning of subsequent injection from the high-pressure fuel feed pump. The pressure for turning out the motor vehicle till the low-speed operation of the internal combustion engine and the high-pressure fuel feed pump can be kept at a controlled pressure. That is, the accumulator pressure can be kept at a low pressure at which neither noise nor knocks will occur. Therefore, the accumulator pressure can be stabilized at a pressure (regulated pressure) necessary for turning out the motor vehicle in case of an emergency without varying to an excessively low pressure below the valve opening pressure, thereby enabling smooth driving of the motor vehicle to a turnout lane in an emergency.
In another aspect, the damper chamber opens at the end face on the spring side of the valve body, being formed in a shape of recess having a larger inside diameter than the sliding bore. The damper chamber is defined by the end face on the sliding bore side of the large-diameter portion of the piston, the inner wall surface of the recess portion, and a stepped portion between the recess portion and the sliding bore.
In another aspect, the pump pressure for turning out the motor vehicle in an emergency because of excessive fuel delivery from the high-pressure fuel feed pump is determined by the outside diameter of the small-diameter portion of the piston and the spring force. It is, therefore, possible to easily set the pressure safety valve closing pressure for decreasing the accumulator pressure after releasing the pressure during an abnormally high pressure. Also, the pressure safety valve opening pressure is determined by the diameter of the valve element seat of the pressure safety valve and the set spring load, thereby enabling easy setting of the pressure safety valve opening pressure necessary for achieving safety.
In another aspect, between the outer peripheral surface of the small-diameter portion of the piston and the sliding bore of the valve body is formed a fuel passage for connecting the damper chamber to the valve hole when the valve element has moved upward over the predetermined value from the valve seat. For instance on the outer peripheral surface of the small-diameter portion of the piston is formed a cutout portion for forming the fuel passage therein, so that if the small-diameter portion of the piston is present within the sliding bore of the valve body when the valve element has risen over the predetermined value from the valve seat, the fuel can be released from the inside of the accumulator through the valve hole and the fuel passage.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.